Plate tectonics
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Plate tectonics Plate tectonics Presentation Transcript

  • Plate tectonics  M. Lutta
  • 9.1 Continental Drift An Idea Before Its Time  Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent. • Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
  • Breakup of Pangaea
  • 9.2 Plate Tectonics Earth’s Major Roles  According to the plate tectonics theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer. This layer is known as the lithosphere. • A plate is one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere.
  • 9.2 Plate Tectonics Types of Plate Boundaries  Divergent boundaries (also called spreading centers) are the place where two plates move apart.  Convergent boundaries form where two plates move together.  Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.
  • Three Types of Plate Boundaries
  • 9.3 Actions at Plate Boundaries Divergent Boundaries  Oceanic Ridges and Seafloor Spreading • Oceanic ridges are continuous elevated zones on the floor of all major ocean basins. The rifts at the crest of ridges represent divergent plate boundaries. • Rift valleys are deep faulted structures found along the axes of divergent plate boundaries. They can develop on the seafloor or on land. • Seafloor spreading produces new oceanic lithosphere.
  • Spreading Center
  • 9.3 Actions at Plate Boundaries Divergent Boundaries  Continental Rifts • When spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift.
  • East African Rift Valley
  • 9.3 Actions at Plate Boundaries Convergent Boundaries  A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.  Oceanic-Continental • Denser oceanic slab sinks into the asthenosphere. • Pockets of magma develop and rise. • Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent. • Examples include the Andes, Cascades, and the Sierra Nevadas.
  • Oceanic-Continental Convergent Boundary
  • 9.3 Actions at Plate Boundaries Convergent Boundaries  Oceanic-Oceanic • Two oceanic slabs converge and one descends beneath the other. • This kind of boundary often forms volcanoes on the ocean floor. • Volcanic island arcs form as volcanoes emerge from the sea. • Examples include the Aleutian, Mariana, and Tonga islands.
  • Oceanic-Oceanic Convergent Boundary
  • 9.3 Actions at Plate Boundaries Convergent Boundaries  Continental-Continental • When subducting plates contain continental material, two continents collide. • This kind of boundary can produce new mountain ranges, such as the Himalayas.
  • Continental-Continental Convergent Boundary
  • Collision of India and Asia
  • 9.3 Actions at Plate Boundaries Transform Fault Boundaries  At a transform fault boundary, plates grind past each other without destroying the lithosphere.  Transform faults • Most join two segments of a mid-ocean ridge. • At the time of formation, they roughly parallel the direction of plate movement. • They aid the movement of oceanic crustal material.
  • Transform Fault Boundary
  • Mantle Convection Models